Methylene blue as an indicator for sensitive electrochemical detection of adenosine based on aptamer switch

In this paper, a simple, label-free and regenerative method was proposed to study the interaction between aptamer and small molecule by using methylene blue (MB+) as an electrochemical indicator. A thiolated capture probe containing twelve bases was firstly self-assembled on gold electrode by gold–sulfur affinity. Aptamer probe containing thirty two bases, which was designed to hybridize with capture DNA sequence and specifically recognize adenosine, was then immobilized on the electrode surface by hybridization reaction. MB+ was abundantly adsorbed on the aptamer probe by the specific interaction between MB+ and guanine base in aptamer probe. MB+-anchored aptamer probe can be forced to dissociate from the sensing interface after adenosine triggered structure switching of the aptamer. The peak current of MB+ linearly decreased with the concentration of adenosine over a range of 2 × 10−8–2 × 10−6 M with a detection limit of 1 × 10−8 M. In addition, we examined the selectivity of this electrochemical biosensor for cytidine, uridine and guanosine that belonged to the nucleosides family and possessed a similar structure with adenosine. The peak current of MB+ slightly decreased even then 1 mM cytidine, uridine or guanosine was added to reaction cell for 2 h, which confirmed this biosensor had a good selectivity for adenosine. After each of detection, the electrode was immersed into aptamer solution for regeneration. The recovery of the electrochemical signal of MB+ indicated the sensor surface of electrode was successfully regenerated.